1. Introduction
This invention relates to wetting the surface of the eye and/or an ocular prosthesis, providing mechanical lubrication therefor, reducing the evaporation of fluid from the surface of the eye and if desired, delivering a medicant to the ocular surface. More particularly, the invention relates to a composition capable of augmenting and maintaining a stable tear film over the ocular surface and/or delivering a medicant to said surface without causing substantial blurring of vision. In a preferred embodiment of the invention, the invention relates to an ophthalmic composition for dry eye treatment. The invention is especially useful for treatment of individuals wearing ocular prostheses such as contact lenses, as the composition of the invention wets and provides lubrication for both the ocular surface and the surface of the prosthesis in contact with the ocular surfaces.
2. Description of the Prior Art
It is known in the art that an aqueous tear film extends over the ocular surfaces and maintains the ocular surface moist and lubricated. It is also known that dehydration of moisture from the eye may result in discomfort. Further, it is known that compositions are available in the market intended for dry eye treatment. These compositions are primarily aqueous materials that supplement the tear film.
The feeling of discomfort resulting from a dry eye condition may include ocular dryness, grittiness, burning, soreness or scratching, dependent upon the subject and the condition of the subject. Proposed causes for dry eye, treatment and symptoms are described in a compendium of papers edited by Holly, The Preocular Tear Film in Health, Disease, and Contact Lens Wear, The Dry Eye Institute, Lubbock, Tex. 1986, incorporated herein by reference.
The most common treatment for dry eye involves temporary alleviation of dry eye symptoms by topical application of a tear substitute that adds a large volume of liquid to the anterior surface of the eye and related adnexa. Typical tear substitute compositions comprise water soluble polymer solutions. Examples of such solutions include saline solutions of polyvinyl alcohol, hydroxypropylmethyl cellulose or carboxymethyl celluloses. U.S. Pat. No. 4,421,748 teaches an artificial tear composition comprising an aqueous hypotonic solution of lecithin and a viscosity adjusting agent such as a solution soluble cellulose.
Methods used to quantify the effectiveness of tear substitutes for dry eye treatment solutions have not been standardized, and many methods used to quantify the results obtained using such tear substitute compositions are often inaccurate. For this reason, it is known that reported relief of dry eye symptoms using known tear substitutes varies considerably from subject to subject, and regardless of the method used to quantify relief using a tear substitute, relief often does not exceed several minutes.
The symptoms associated with dry eye are often exacerbated with subjects using ocular prostheses such as contact lenses. In some cases, contact lens intolerance is caused in part, or in total, by the condition of dry eye and its symptoms. Further, the rate of evaporation from the eye is accelerated by the nature of the contact lens surface and the physical presence of the contact lens results in meniscii formation with additional physical and evaporative effects, even with subjects having an adequate tear film. For many subjects, contact lens intolerance is not overcome by topical application of tear substitutes. Therefore, there is a need for improved compositions and processes for treatment of the dry eye condition and for improving tolerance to ocular prostheses.
An improved composition for dry eye treatment is the subject of U.S. Pat. No. 4,914,088 incorporated herein by reference. This patent teaches the use of charged phospholipids for the treatment of dry eye symptoms. The addition of a charged phospholipid to the eye assists in replicating the tear film that would naturally occur in the eye. In accordance with the patent, the phospholipid composition, preferably in the form of an aqueous emulsion, is topically applied to the eye where it is believed to disperse over the ocular surface and form a film that replicates a lipid layer that would be formed by the spreading of a naturally occurring lipid secreted principally from the Meibomian glands during blinking. Because the phospholipid, when applied to the eye, carries a net charge, it is believed that aligned molecules repel each other preventing complex aggregate formation thereby resulting in a stable phospholipid film. The patent speculates that the film formed from the charged phospholipid assists in the formation of a barrier film reducing evaporation of the aqueous layer, thereby preserving the tear film.
In copending U.S. patent application Ser. No. 07/529,657, filed May 29, 1990, a further improvement in dry eye treatment is disclosed. In accordance with the disclosure of said application, the dry eye treatment composition of U.S. Pat. No. 4,914,088 is improved by the addition of an essentially non-polar oil to the eye treatment composition. The oil is added to improve the performance of a dry eye treatment composition by increasing the longevity of the tear film formed on the eye following addition of the dry eye treatment solution, presumably by providing and/or thickening the dehydration barrier (the oil layer) on the outer surface of the tear film. Thus, the oil increases the efficacy of the dry eye treatment solution and reduces performance variability from subject to subject.
The use of the dry eye treatment of the referenced application assists in overcoming dry eye symptoms as reported in the application. However, when using the procedures and composition of the application, some subjects experience blurring following addition of the treatment composition containing the oil. The time required for the blur to clear is often unpredictable. In addition, relief of dry eye symptoms was found to vary somewhat from patient to patient.